While Auckland's population is steadily increasing, school leavers are turning away from teaching as a profession.

After four years' study, pay for teachers starts at about $43,000 and reaches about $70,000 after 5-6 years, said Mr Bush.

"Previously, people would go to university, get a degree, get a job and get good money. Nowadays, kids have got a raft of opportunities out there.

"The economy is doing well and there's a lot more pay out there in other professions."

But teachers are also finding it too expensive to live in Auckland - some are commuting four hours a day to their jobs - and leaving the region for other centres.

"That's four hours of teacher preparation gone," said Mr Bush. "Everyone thinks teaching is a 9-3 job, but it's not.

"It's 8-5 job, plus most teachers will do work at home after dinner or whatever."

Mr Bush said relief teachers were also hard to find. With about 1000 relievers needed each day, only about 60-70 percent of those positions were being filled and some schools were forced to put management back into classroom to make up numbers.

"This is a perfect storm for Auckland," he said. "Three years ago, we had inner city schools that had been getting 100 applicants for a job, but that had dropped to 10-15 applicants.

"We told [the Ministry of Education] then that there was a crisis about to hit - we are now at that point."

Mr Bush said while the situation was dire, it was not yet at the point where schools had to cancel classes.

"But there are principals out there being very, very cautious, going through this term, because they know if a teacher resigns through this term, they will be struggling next year."

In previous times of shortage, New Zealand has recruited from overseas, with British teachers filling the void during the 1990s.

Education Ministry deputy secretary Ellen MacGregor-Reid told Newshub her organisation was concerned that teacher supply in some subjects, including science, technology, maths and te reo Maori, was "tightening" and certain locations, including Auckland, were feeling the pinch.

"For this reason, a number of incentives, worth over $19 million, are being implemented," she said.

"We've established a teacher quality and wellbeing working group, with a number of sector groups, and are embarking on a comprehensive workforce strategy, looking at short-term supply challenges, as well as the development of a longer term plan."

But Ms MacGregor-Reid also suggested many of the unfilled roles were actually for next year's first term.

"The wider available data shows that the overall number of teachers has increased. The number of registered teachers with a practising certificate to teach in New Zealand has grown from approximately 90,000 in 2007 to 101,000 in 2017.

"Payroll data also tells us that retention rates remain high, at over 92 percent nationally and in Auckland."

The ministry also had several initiatives aimed specifically at the Auckland market, including an Auckland Beginning Teacher Project to find expert junior class teachers, a specialised recruitment agent and an international relocation grant to help overseas teachers move to New Zealand.